It is desirable to “superfat” (add free fatty acid) to fatty acid soap bars because they provide a creamy, tactile feel desirable to many consumers.
One method of superfattying a bar is to simply add free fatty acid to soap. However, the addition of free fatty acid is generally more expensive than producing fatty acid in-situ via production of organic or inorganic acids from their counterpart salts. Also, when adding free fatty acid to soap the levels are limited (e.g., less than about 8% by wt. bar composition) because the free fatty acid may cause the bar to be tacky (sticky and prone to leaving residue when touched); may cause discoloration; and/or may reduce lather (see U.S. Pat. No. 6,218,348 to Aronson et al. (column 4)).
Another way of introducing free fatty acid into a soap bar is to form the free fatty acid directly in the reaction from the fatty acid soap (i.e., the “soap”, which is a salt of fatty acid, is broken down to free fatty acid upon release of the counter electrolyte salt). Typically such a reaction may be precipitated by use of an acid (e.g., citric acid) whose pKa is less than that of the fatty acid soap. Because of its lower pKa, the acid will “attract” the electrolyte salt (e.g., sodium) from the fatty acid soap thereby forming free fatty acid and a salt of the protic acid used to cause the precipitation (e.g., sodium citrate in the case of citric acid addition).
One problem with this method of generating free fatty acid from the soap is that, as elevated levels of protic acid salts are produced (e.g., production of sodium citrate during the production of free fatty acid from the soap), efflorescence (i.e., the appearance of salt crystals which both provide a negative visual and tactile cue) can occur.
U.S. Pat. No. 6,218,348 to Aronson et al., for example, describes bars containing free fatty acids, polyalkylene glycol and specific salts of protic acid (i.e., salts having pKa less than 6; the lower the pKa, the stronger the acid) wherein said bars are said to have beneficial sensory properties and can improve skin. The patent, however, fails to recognize that the protic acid salts may cause efflorescence during the in situ production of fatty acid from the soap; and there is, of course, no discussion of how to deal with this issue.
One solution to the problem has been to partially generate free fatty acid (i.e., at a level that there is not enough salt formed to cause efflorescence) and then adding free fatty acid to make up the difference to a desired higher level where such efflorescence will normally have been detected. This method is quite costly.
Unexpectedly, applicants have found that when a sodium aluminate solution (precipitating aluminum hydroxide in final bar composition) is added during processing (e.g., to reverse titrate excess levels of free fatty acid generated by the use of protic acid having pKa lower than soap), the resulting generated aluminum hydroxide acts to hinder or eliminate altogether the efflorescence normally caused by production of the precipitated protic acid salt (e.g., sodium citrate).
The aluminate technology of reacting fatty acid or acid precursor and, for example, aluminum containing alkaline material (e.g., sodium aluminate) is not new. In U.S. Pat. No. 6,207,636 to Benjamin et al., for example, a low total fatty matter ((TFM); the term is used to denote % by wt. fatty acid and triglyceride residue percent, without taking into account accompanying cations) bar is prepared comprising 25 to 75% TFM, 9.0 to 16% colloidal aluminum hydroxide (A-gel), 12 to 52% water, optional benefit agent and conventional additives.
There is no disclosure, however, of soap/free fatty acid bars or of the use of protic acid having pKas lower than fatty acid in the fatty acid soap; and there is no disclosure of the use of such protic acids to produce free fatty acids from the soap. There is also, therefore, no teaching or disclosure of aluminate (and precipitated aluminum hydroxide) used to resolve the problem caused by protic acid salt precipitation.
Similarly, U.S. Pat. No. 6,310,011 to Behal discloses TFM bars comprising a colloidal aluminum hydroxide phosphate complex, but neither teaches nor suggest bars where both specific salts of protic acid (having pKa lower than the fatty acid soap) and aluminum hydroxide are found in the final bar, or that use of the hydroxide ameliorates the efflorescence problem caused by the protic acid salt generated even as free fatty acid is being produced from the fatty acid soap.
The present invention represents a novel marriage of the two technologies resulting in novel composition, novel processes to make the compositions as well as unexpected amelioration of the efflorescence problem.